1. Field of the Invention
The present invention relates to session transfer in a Converged Internet Protocol Messaging (CPM) System, and more particularly, to session transfer between devices based on temporary storage in a CPM system.
2. Description of the Related Art
In the existing mobile environment, terminals send intermittent messages such as Short Messaging Service (SMS) messages and Multimedia Messaging Service (MMS) messages. However, many users increasingly expect new messaging services in which they can easily have a dialog using the messenger application in the wired environment. Hence, an Instant Messaging (IM) service has been introduced in terminals and networks based on a Session Initiation Protocol/Internet Protocol (SIP/IP) Core network. Moreover, a Push to talk over Cellular (PoC) service and system based on the SIP/IP Core network has been developed to meet the needs of customers and businesses for Push To Talk (i.e., walkie-talkie). Along with the rapid change in the communication industry, many users increasingly desire to handle different types of received messages in an integrated manner.
Considering these facts, Open Mobile Alliance (OMA), a standards organization, which establishes international private standards of mobile solutions and services, is currently developing standard technologies for Converged IP Messaging (CPM) implemented based on the SIP/IP Core network.
The CPM service is an IP Multimedia Subsystem (IMS)-based messaging service, and its concept provides the existing SMS and MMS services based on the Internet Protocol (IP) in an integrated manner. While the current messaging service enables transmission/reception only in limited networks and terminals, CPM may provide IP-based united messaging services regardless of the terminal type, media type (i.e., content of the message), network type and service type.
One of the many features of the CPM service is that users can access the messaging service using many different devices simultaneously. For example, one user may be provided with the service by using a device A-1 and a device A-2 at the same time. If the user is initially communicating with remote device B (remote user) using device A-1 but desires to continue communication using device A-2 while he is connected to the remote device B, the session that was connected through device A-1 (source device) needs to be transferred to device A-2 (target device). The described procedure is called “session transfer.”
In order to maintain a high quality of communication services during the session transfer, a detailed operational procedure for seamless session transfer is required so that neither the source user nor the remote user are aware of the session transfer.